Ok this question has probably been asked a million times already!
I've done some research, looked on here, even asked the makers of the filaments I've bought for their advice-
And what do I get for my time...
A mixture of conflicting advice, I know that Cura doesn't have a profile as such for the TAZ 6 and that is causing problems for me.
There have been up to three possible profiles that can be used because of similar material properties:
Ngen, Inova 1800 and Colorfabb XT, they all give slightly different values- not a problem when setting up, however some other problems then arise...
The makers of my filaments have greatly different recommendations, Real Filaments says: melting point 190-245'C and a bed temperature of 20-35'C, However...
Technology outlet's filament says: Temp. 220-260'C (Ideal 245'C)and bed temp.60-80'C.
A bit of difference? some say use a stick of PVA glue and other say not- some say fans on and of course others say don't- (but most average out at 70%) however the Cura profiles all have the fans on at 100%...
Mighty confusing?...
Some advice on here recommends temperature start at 230 -235'C and the bed at 85? fans at 75%?
And another says: 240'C, flow at 90% 60'C bed at 0.2mm and 245'C/60' bed, bed removal at 45', 0.35mm at 255'C, 1st layer at 0.4mm and low infill. 248'C, 80' bed, No fan if room is cool, fan set to 70% if room is warm, slower speed?
Some say you need an enclosure others say not...talk about going round in circles...
Right I need to print out lego part 3024, 3032 and 3939(at 300% size) in translucent PETG (because they where the only ones I could find in those colours available for that particular model-918)
They need to be as clear as possible (although I know 100% is not possible so 70-90%+ would be nice)
Fine printing at 0.18mm or less and 100% infill to get them as near clear as the TAZ 6 can do.
So can I modify an existing profile and use it for PETG just for now until someone comes along and up dates Cura? Or do I need to write a new one from scratch?
Oh and I'm using a standard extruder that came with the machine- nothing fancy...

I use the Inova 1800 profile for PETG and have been getting great results with a standard extruder on a Mini. I was having some pretty big failures when trying to print it in the 230C -235C range and also had some massive clogs happen. I was able to get a nice PETG print at 245C, however different manufacturers might have a different temperature range based on what they use to make the filament. I've had great luck with Chroma Strand Labs PETG.

Also, it seems like translucent filaments become more translucent at a high layer height.

Thank you for answering.
Sorry for a being a right pain...
High layer height?,(I'm unfamiliar with this setting- I've never needed to adjust this before) Would the surface of the printed piece suffer with the quality of the finished thing. Is there a way round that factor too? (like using acetone on ABS) Does PETG have its own smoothing surface chemical? (if indeed this is a problem in the first place?)
I suppose I could experiment with tiny pieces on different profiles and post them on here- hopefully my mistakes/successes would be useful to someone on here too. (although i was slightly concerned there is no profile for PETG on Cura?- there does seem to be quite alot of it on the market- with similar materials also available too?)

High layer height?,(I'm unfamiliar with this setting- I've never needed to adjust this before)

High layer height doesn't refer to a setting, it refers to the value you have set for the layer height. A layer height of 0.3 is higher than a layer height of 0.1 so I believe a different way to word Ehoff's statement would be that as you increase the layer height, translucent filaments become more translucent.

B-morgan is correct about what I was saying. You can adjust the layer height under the Custom slider in Cura LE, once you slide the slider from Recommended to Custom, you will see quite a few tabs appear. You will select the Quality tab, and that is where you can change the layer height. Smaller layer heights are good for higher detail prints, but translucent filament tends to become more translucent when you give them larger layer heights.

Brent, how do you deal with the different print heads when developing profiles? I imagine there must be a variance.

There is definitely a difference between tool heads, usually related to cooling and acceleration settings. More weight requires slower movement, more powerful fans require a little less cooling, etc. We actually have a full time R&D tech devoted to material testing and profile development, who used to do all of our slicing for the cluster of 155 printers. We also have a printer on every employees desk, which we use to test and verify new materials and profiles. One of the key aspects is being reliable and repeatable across multiple printers, otherwise we will not consider it a quality profile.

You will also notice over the next few months, that many more materials will be appearing in the "experimental" section. We are working closely with filament vendors to get profiles for filaments that we do not carry and sell into Cura LE. We currently have multiple PETg profiles, along with newly added MatterHackers PRO and Build series PLA. We will keep rolling in the filament manufacturers recommendations, and once we have a chance to verify the profile ourselves we will move it over to the regular categories. If anyone has any feedback on how well the profiles work, please let us know and we can get updates in for future releases.

Whew, looks like I got a little long winded there! I hope this helps, and feel free to let us know if you have any other questions!

(Now if only there was a way to migrate those profiles to Simplify3D )

I have a profile I use on S3D for my Taz 5 with a .35 nozzle. I've been fine tuning it for Maker Geeks PETG and it's still a WIP of course, currently my bridge settings are still in flux, PETG doesn't like to bridge to my standards.

I print 99% of the time with this filament so I've been able to get some great settings out of it if you're interested.